Fingerprinting is used to protect copies of fingerprints left at a crime scene. There are three types of fingerprints: plastic, visible, and latent. Different approaches are used to lift each type of print, including powders and cyanoacrylate ester. Fingerprinting has become more sophisticated, allowing for the recovery of previously undiscovered prints.
Fingerprinting is the process of protecting copies of fingerprints left at a crime scene. Successfully lifting a set of footprints increases the chance of determining who was at the scene in the recent past, which in turn adds to the evidence needed to identify and justify the arrest of the perpetrator. There are several approaches to fingerprinting used around the world, including procedures that allow fingerprints to be taken that are invisible to the naked eye.
To understand the idea of fingerprinting, it is important to note that there are three basic types of fingerprints that can be present at a crime scene. Plastic prints are any set of prints that are left as imprints on a soft material. Prints of this type can appear on a bar of soap, in the dust left on a tabletop or in the imprints left by handling a wax candle.
Visible fingerprints are fingerprints that are left after fingers come into contact with some type of substance that leaves an impression when the individual touches a surface. For example, visible footprints are left when blood contacts the hands and the individual touches a doorknob, wall, or tablecloth. Along with blood, substances such as wet paint, ink and even grease on the hands can lead to clear sets of fingerprints which are very useful for identification.
The third class of fingerprints, known as latent or invisible fingerprints, are those that are left when fingers come into contact with objects such as glasses, ashtrays or other surfaces. Prints of this type develop when perspiration or natural skin oils come into contact with the surface. While not always immediately visible, using fingerprint powder can often cause fingerprints to appear.
Once a set of fingerprints is identified, the actual fingerprinting process begins. With plastic and visible prints, digital photographs of the prints are usually taken. Along with photographic proofs, there are several powders that can be applied directly to the print. Special paper is then applied to give an impression of the print. Great skill is required when lifting prints in this way, as it is very easy to smudge the print and thus render the proofs useless. For this reason, only specially trained law enforcement agencies engage in this type of fingerprinting.
A commonly used strategy to lift latent prints involves the use of cyanoacrylate ester, an ingredient found in many quick-drying glue products. This process involves placing the object suspected of containing fingerprints in a controlled environment along with a measured amount of the compound. When cyanoacrylate ester is heated, it begins to release fumes. Over a period of several hours, exposure to the fumes will cause the prints to become easily visible, making it easier to photograph them before attempts are made to copy the prints onto another medium.
The exact approach to fingerprinting will also depend on the media containing the print. The powders work well on smooth surfaces, while the use of cyanoacrylate esters or even products like silver nitrate are more effective with ribbed or otherwise non-smooth surfaces. Over the years, the art of fingerprinting has become more and more sophisticated. Today it is possible to recover fingerprints that would never have been found in decades past, a reality that increases the ability of law enforcement agencies to gather relevant evidence needed to solve crimes.
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